SOURCES OF ENERGY AND MATERIALS 111 



which inchide raw plant food are generally adequate, but cooking in 

 vessels exposed to air usually destroys much of the antiscorbutic effect. 



Vitamin A, itself colorless, can be split off, in the human body, from 

 the yellow pigment carotene found in carrots and many yellow and green 

 vegetables. Its formula is C20H30O. Severe lack of it in the diet leads 

 to a dry, ulcerated condition of the cornea of the eye known as xeroph- 

 thalmia (Fig. 92). Milder deficiencies cause abnormalities of epithelial 

 membranes and retard growth. Vitamin A is also used by the retina 

 of the eye in the synthesis of visual purple, one of the light-sensitive 

 pigments, and was administered during the war to night-flying pilots to 

 improve their vision. Being soluble in fats (as are two other vitamins, 

 D and E), vitamin A is obtainable in liver oils and in such foods as milk, 

 butter, and egg yolk. Manufactured butter substitutes are usually 

 fortified by the addition of this vitamin. 



What was originally called vitamin B eventually proved to be a 

 collection of different substances, enough alike to be hard to separate, 

 and occurring mostly in the same natural foods. This group, consisting 

 of seven or more vitamins, is now known as the B complex. Only the 

 more important of these can be mentioned here. Lack of thiamin (Bi) 

 causes polyneuritis, which in man is usually named beriberi. This 

 disease involves degeneration of the nerves, causing progressive paralysis. 

 Along with paralysis go retarded growth and loss of appetite and vigor. 

 Intravenous injection of Bi into polyneuritic animals restores normal 

 muscular movement in as short a time as one hour. The formula of 

 thiamin is C12H16N4SO. One of its sources in food is in cereals, especially 

 the outer seed coats. For this reason polished rice, in which the seed 

 coats are removed, and highly refined wheat flours (as contrasted with 

 whole wheat) are poor in thiamin. It is common practice now to add 

 thiamin in the manufacture of white flour. Other natural sources of 

 thiamin are meats, especially pork, and yeast. 



A second member of the B complex is riboflavin (C17H20N4O6), called 

 also B2. It is found in the same foods as Bi and the other vitamins of 

 this group. Lack of it induces a predisposition to cataract, loss of 

 weight, and scaliness of skin around the ears and mouth. 



Closely associated with the other B vitamins is niacin (C6H5NO2), or 

 nicotinic acid. Lack of it is the principal cause of pellagra, which is 

 characterized by dermatitis (eruption of the skin) and diarrhea. As a 

 pellagra preventive, niacin has come to be called vitamin P-P. The 

 disease is still common in southeastern United States, where corn, 

 molasses and meat are the staple diet. Niacin is manufactured and is 

 available to prevent pellagra, but is not yet in sufficiently wide use. The 

 dermatitis feature of pellagra may be due to lack of Be, or pyridoxin, 

 which is frequently absent from the pellagra-producing diet. 



